Winches for pulling cable, rope, chains and the like have been employed in many situations where it is desirable to pull long lengths of cable over a long distance. In addition to the common use of winches on tow trucks and the like for pulling vehicles from off-road locations, where electric winches are adequate, the more difficult industrial applications involve cables and the like of substantial weight per unit length, such as power cables and anchor chains, for example.
A winch is, in its simplest form, a drum on which cable and the like is wound or unwound, where the drum is driven by a motor. Many winches used with heavy cables such as electric power cables employ gears and transmissions for converting shaft speed into pulling power. In these devices, higher drum speed reduces the power available to turn the shaft on which the drum resides. This results in a trade-off which is acceptable only when one or the other of the factors of speed or pulling power is in excess.
Hydraulic motors have been used in some winch applications, where a fluid under pressure is introduced into a cylinder to drive a piston and thus convert hydrostatic energy to movement, usually rotational by driving a crank shaft which in turn drives the shaft on which the drum is mounted. . In most cases the hydraulic motor is designed to drive a shaft, usually in combination with a transmission or gear box.
One form of hydraulic motor that has found use in industry is the low speed/high torque hydraulic motor, although it has not been applied to winch devices because of certain drawbacks listed below. These low speed and high torque hydraulic motors come in two basic forms and in a variety of designs. The motors either are gear reduction motors or radial piston motors. In the former, high speed motors are reduced using a complicated series of gears to lower the speed and achieve higher torque. In the latter, various schemes for moving fluids around the axis of a crankshaft have been provided. Neither is suitable for use with, for example, a compact winch design mounted on a utility company vehicle used for installing and removing heavy electric power cables and the like.
Vane motors employ pressure against a plurality of vanes riding on a ring cam to form sealed chambers that carry fluid through the device, optimally at low pressure. The major disadvantage is that there are too many leakage paths. Rolling-vane motors sequence fluid flow to put high pressure against trailing surfaces and low pressure against leading surfaces, but are limited in displacement.
There are also a variety of piston motors. Radial piston motors have a wide displacement range and are very efficient in medium or high displacement ranges. Cam type radial piston motors are less efficient and have difficulty at low speed. Axial piston motors are effective and have good starting torque characteristics. Two sources of heavy duty hydraulic motors are Nutron Motor Co., Inc. in Eliot, Maine, which produces a radial piston hydraulic motor under the MHA series, and Kawasaki Precision Machinery, Inc. which produces radial piston hydraulic motors at its Staffa facility in Plymouth, England.
One of the principle drawbacks to hydraulic motors is that the commercial designs are extremely large for the power that is produced. Both the space or volume taken up by such motors and the weight that is needed are so great as to be seen as drawbacks or handicaps when selection of a motor is being made. In order to have useful torque in industrial applications, such as in heavy equipment, moveable boat and lumber lifts, end loaders, winches, and other hub drive designs, great amounts of power is needed. However, all presently known designs are not capable of effectively using the power of a short stroke, high displacement motor arranged within a compact area or motor volume so as to be adapted to the device of interest.
It would be of great advantage if an improved hydraulic motor for use with winches could be provided that would deliver the same or greater power using less space and having less weight than conventional motors which have been described.
In addition, it would be an advance in the art if high torque, low speed motors could be designed that did not require the use of multiple reducing gears to translate high speed motion into low speed, high torque output.
Finally, it would be of significant advance if a winch device with a hydraulic motor could be provided that had the capability of self braking, so that no additional brake device would be needed for the motor, and the equipment to which it is attached, to remain motionless while supporting the full weight of the load being driven. In other words, it would be a great advance if the motor could stop at any pre-selected point and support the load attached thereto without the use of additional brake elements.
Accordingly, it is an object of the present invention to provide a winch device having a drum driven by an hydraulic motor capable of operating under high torque and low speed, such motor being suitable for operation in a smaller space than prior art designs.
A further object of this invention is to provide a winch device having a drum driven hydraulic motor capable of producing high torque and low speed without the need for multiple reducing gears to translate high speed motion into the resultant high torque and low speed.
Yet another object of the present invention is to provide a winch device having a drum driven hydraulic motor having fixed displacement of substantially larger capacity.
Other objects will appear hereinafter.